10% growth is still strong, but the drumbeat of downward estimate revisions is bad news for Microsoft, whose Windows operating system still powers more than 90% of personal computers worldwide, and which is the company's biggest and most profitable product, earning $12.7 billion on $18.8 billion in sales over the last four quarters.

Microsoft is hoping that Windows 8 will make it competitive in the tablet market -- the OS is being redesigned to run on the low-powered ARM processors that run most tablets, and will have new interface elements for touch screens as well. But Windows 8 probably won't be commercially available until late 2012.